I believe carrying "the internet" across a WUG changes it's status from a license-exempt network to one that requires another form of license (ECS/ECNS etc).

But what would ICASA/ECA stance be if a WUG were to connect to an INX (Internet Exchange) via e.g. BGP?

In the specific case I envision, the IX would not give the WUG routes to the global internet, just local independent networks. (I.e. you could check network-accessible resources on your work PC/server(s)), probably via NAT through a limited number of "real world" IP addresses. Categorically a non-transit peering session.

BGP ASNs would be in the private use range (64512 through 65535, although in this case from 65500 up).

The specific INX I'm thinking of is pretty small, but would be very useful for members of the community I live in to have access to.